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Latest USSC Foundation Study Now Available: Parallel Sign Legibility and Letter Heights
Bristol, Pennsylvania—Another landmark scientific study designed to provide specific information and workable real-world calculation procedures concerning the vital issues surrounding on-premise sign legibility has now been completed. This latest research project represents the twelfth in the impressive line of sign-oriented research studies conducted by the USSC and the USSC Foundation and is now available from USSC.
Entitled On-Premise Signs, Determination of Parallel Sign Legibility and Letter Heights, the study fills a critical gap in the available research by providing a model for calculating the size of letters and signs, mostly flat wall signs and similar installations, which are parallel to a motorist’s field of vision.
Since 1996, the USSC and the USSC Foundation have taken a leading role in disseminating research information and research-based legibility tables to help sign designers determine appropriate on-premise sign sizes and letter heights, most of which are covered in the USSC On-Premise Sign Standards publication. These indices and standards were developed by USSC to ensure adequate readability of signs that are mounted perpendicular to the roadway, notably freestanding signs. On-premise signs, however, are often oriented parallel to a driver’s line of sight, and this type of sign is more difficult to read, particularly under heavy traffic conditions.
A parallel sign is harder to read because its orientation or tilt with respect to a driver makes it impossible to se the sign face at certain distances and offsets. When the driver can see the sign face, the content is often foreshortened and distorted. The driver must get close to the sign in order to increase the viewing angle to the point where the sign becomes legible.
However, as drivers approach the sign, the time they have to read it gets shorter, while the sign moves further into their peripheral vision. Therefore, parallel signs must be read using a series of very quick glances at large visual angles during small windows of opportunity. Because of this, letter heights developed for perpendicular signs, where drivers have more time and can take longer straight-ahead glances, do not provide adequate parallel sign legibility.
The current research report is designed to rectify this legibility condition by providing a rationale for, and the development of a mathematical model that results in letter heights for parallel mounted signs. This model can easily be applied to the current USSC Legibility Standards and Legibility Index so that the letter heights developed for perpendicular signs form the basis for the larger letter heights necessary for adequate viewing of parallel signs with various lateral offsets. The publication offers formulae for calculation of the parallel letter heights, usually three times the height of perpendicular letter heights, as well as easy-to-use letter height lookup tables for many typical parallel sign scenarios.
Copies of the study are obtainable from USSC by calling 215/785-1922 or visiting www.ussc.org, under “Publications.” Cost is $25 per copy ($10 per copy to USSC members) plus shipping.
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